The power factor of an AC (alternating current) electric power system is defined as the ratio of the real power to the apparent power, and is a number between 0 and 1. In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred, and the higher currents increase the energy lost in the distribution system.
Linear loads with a low power factor can be corrected with a passive power factor correction circuit. Non-linear loads, such as rectifiers, distort the current drawn from the electric power system. In such cases, an active or passive power factor correction circuit may be used to counteract the distortion and raise the power factor.